In a cut-off die set of the double cut type, a notching blade is caused to move across and notch the upper surface of the tubing prior to entry of the shearing blade into the upper tube wall. This prenotching eliminates dimpling or collapsing of the tube wall by the shearing blade, thus eliminating the need for reshaping the ends of the tubing after the cutting operation.
The notching apparatus typically comprises a notching blade fixed or mounted to a notching blade holder which is mounted to a cross slide assembly. Cross-slide assemblies are known, see U.S. Pat. No. 4,766,792. The cross slide assembly is operated by the upper platen of the die set by way of a mechanical cam and cam follower. The association is such that vertical travel of the upper platen of the die set causes the notching blade to travel through a transverse path perpendicular to the axial path of the tube. Both thrust and "pull across" motions are known. See for example U.S. Pat. Nos. 4,109,555 and 4,294,147.
Presently, the notching blade holder is mounted to a guideway fixed to the cross-slide assembly, wherein the guideway is adapted to receive and retain a slide member. The slide member is attached to the notching blade holder by screws so that the blade holder can be adjusted for different notching depths and for different tubing diameters. When rotated, the screws urge the slide member into contact with the guideway the result being to clamp the notching blade holder to a fixed position in the guideway. Varying the height of the notching blade relative to the tube path requires the operator to loosen the slide member clamping screws in order to release the slide member and enable repositioning of the holder. Once repositioned, the operator must retighten the slide member screws. This method of adjustment can result in inaccurate adjustments and is time consuming as the space limitations in the die set act to prohibit easy access to the adjusting screws.
Normally in the standard "pull across" die set when the die is in the open position allowing the tube to pass through the clamping jaws the notching blade is positioned across and over the upper surface of the clamping jaws making removal of the clamping jaws difficult. To change the clamping jaws, the operator must remove the notching blade holder to gain the access needed to change the clamping jaws. The additional requirement of removing the notching blade holder makes changing the clamping jaws a time consuming procedure.
At times the vertical cut or guillotine blade is broken during the cutting operation and remains lodged in the clamping jaws. When the die operates in the reverse manner and attempts to return the notching blade to the pre-cut position, the notching blade is prevented from returning by the broken guillotine blade lodged in the clamping jaws, thus resulting in a catastrophic failure of the die set. This failure requires shutting down the mill to replace at least portions of the die set assembly.
The notching blade which performs the cutting operation eventually succumbs to wear and must be replaced. To replace the notching blade, the notching blade must be unbolted from the notching blade holder and a new blade rebolted to the holder. Again a time consuming process.
As indicated, time is of the essence in the tube cutting industry, tubing continuously emanates from a tube mill at a high rate of speed. Thus, any problems, delays or shut downs due to repair or replacement of the cutting equipment results in lost production and revenue to the tube maker. Therefore, any time savings that result from ease in maintenance and/or replacement of parts increases the period the mill can be operational, thus increasing production.